The present invention refers to an extrusion blow molding apparatus for making hollow plastic articles.
An extrusion blow molding apparatus is known of the type having a machine frame which receives a horizontal extruder for vertically extruding a parison via its nozzle head at one end face of the machine frame. A pair of split blow molds is arranged symmetrically at the end face below the nozzle head, with each of the blow molds including a closing unit, a drive unit for horizontally sliding the blow mold underneath the nozzle head for receiving an extruded parison, and a blow mandrel secured to the machine frame above the blow mold.
An extrusion blow molding machine of this type is suitable for making hollow plastic articles of rotationally symmetrical cross section such as e.g. round bottles. Both blow molds are identical final blow molds which are moved horizontally by their respective drive unit from their initial position underneath the associated blow mandrel to a position underneath the nozzle head for seizing the parison being extruded by the nozzle head of the extruder. The parison is then blown to the finished hollow article by the respective blow mandrel after returning the respective blow mold into its initial position, with the finished hollow article being ejected after a suitable cooling period.
Such an extrusion blow molding apparatus is, however, not suitable for producing flat bottles since the construction lacks structural elements for transferring a semi-finished article from an intermediate blow mold to the final blow mold.
The European publication EP-PS 0 256 062 discloses an extrusion blow molding apparatus which includes two blow molds of different configuration for making flat bottles. One of the blow molds is an intermediate blow mold for making a semi-finished article of rotationally symmetrical cross section and the other blow mold represents a final blow mold by which this semi-finished article is transformed to a flat bottle. In this manner, flat bottles can be made through a particular material-saving process and with nearly even wall thickness at least over a major part of its height. The European application EP-PS 0 256 062 is, however, silent about the structure and design of the extrusion blow molding apparatus.
The production of hollow plastic articles of rotationally symmetrical cross section and hollow plastic articles of a cross section deviating therefrom necessitates the availability and operation of a separate extrusion blow molding apparatus for each type of hollow article. Depending on the order situation for both types of hollow articles, long stop periods for one or the other blow molding apparatus can be experienced and is unavoidable.